344 BULLETIN UNITED STATES GEOLOGICAL SURVEY. 



Genera occurring in the Eastern Temperate (Asiatic) Province 46 



Genera of the Mediterranean Province 60 



Genera of the Manchurian Province 65 



Genera common to the Eastern and Western Temperate Province 38 



Genera common to the Mediterranean and Manchurian Province 50 



Maritime genera of the Asiatic coast ^ 8 



Maritime genera of the European coast 6 



Maritime genera common to both EuroxDean and Asiatic coasts 3 



In comparing the North American Eegion with the Europseo- Asiatic 

 Eegion, the following resemblances and differences become apparent : — 1. 

 The number of genera in the EuropsBO- Asiatic Region is rather more 

 than ons-fourth greater than in the North American Eegion, with conse- 

 quently a smaller proportion of circumpolar genera. 2. But this differ- 

 ence results almost wholly from the greater preponderance of peculiar 

 types in the Southern Subregion, due evidently to the immensely greater 

 extent and greater physical diversity of this portion of the Europseo- 

 Asiatic Eegion as compared with the corresponding portion of the North 

 American Eegion. 3. While the colder portions of the two regions have 

 each about tbe same number of genera, which are in great part {nearly 

 two-thirds) common to the two regions, the Warm Temperate (really 

 Subtropical) Subregion of the Europseo- Asiatic Eegion has a far greater 

 number of genera that do not extend to the northward of it than 

 has the Warm Temperate Subregion of the North American Eegion, 

 while a small proportion only (chiefly arctopolitan and subtropicopoli- 

 tan) are common to the two subregions. Hence, 4. The two regions 

 (Europseo-Asiatic and North American) are mainly differentiated (as 

 already noticed) through the presence of genera limited to their south- 

 ern subregions. 



III. — AMERICAN TROPICAL REALM. 



The American Tropical Eealm is approximately bounded by the 

 northern and southern mean annuals of 70° E. Its northern bound- 

 ary has been alread^'^ indicated in defining the southern limit of the 

 North Temperate Eealm, it being concurrent with the southern 

 boundary of the North American Temperate Eegion. The southern 

 boundary of the American Tropical Eealm leaves the Atlantic coast 

 near the thirtieth degree of south latitude, or near the southern extrem- 

 ity of Brazil, but in passing from the coast sweeps rapidly northward 

 till it nearly or quite reaches the Tropic of Capricorn in Northeastern 

 Buenos Ayresj it then bends to the southward and continues westward 

 to the eastern base of the Andes. The Andean chain forms its western 

 limit thence northward to Ecuador, where it crosses the Andean high- 

 lands and is again deflected southward, thus including a narrow belt 

 of the coast region west of the Andes in Northwestern Peru. 



As thus defined, the southern border of the American Tropical Eealm 

 is nearly coincident with the southern boundary of the " Brazilian 



